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From: "m.cencora at gmail dot com" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Subject: [Bug c++/98122] New: [regression] Accessing union member through
 pointer-to-member is not a constant expression
Date: Thu, 03 Dec 2020 13:50:12 +0000
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D98122

            Bug ID: 98122
           Summary: [regression] Accessing union member through
                    pointer-to-member is not a constant expression
           Product: gcc
           Version: 10.2.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c++
          Assignee: unassigned at gcc dot gnu.org
          Reporter: m.cencora at gmail dot com
  Target Milestone: ---

Following code does not compile on gcc-10 and newer in all std C++14-20 mod=
es.

This used to work in gcc-9 and earlier.

union foo
{
    int a;
};

constexpr bool test()
{
    foo f{ .a =3D 42 };

    constexpr auto memPtr =3D &foo::a;

    return (f.*memPtr) =3D=3D 42;
}

// error: accessing value of 'f' through a 'int' glvalue in a constant
expression
//     return (f.*memPtr) =3D=3D 42;
static_assert(test(), "");=